The present invention relates to a wire harness assembly line.
In the above-described wire harness assembly line, an operation chart board for each of the processes is mounted on each of wheeled worktables and conveyed to a operator""s station in a sequence of the processes, and the operator works sequentially on the chart board to complete the product. FIG. 11 shows an example of the conventional wheeled worktable conveyance line that is driven with an endless chain.
As shown in the figure, a straight outbound passage 23 and a straight return passage 24 are installed parallel as conveyance passages of wheeled worktables 21 and both ends are connected with turning parts 25 and 26 making a closed passage, wherein an endless driving chain 22 is installed along the closed passage with the aforenamed wheeled worktables linked with the chain 22 in the order of the processes and moved in one direction with chain 22 driven by a motor MC. Operators m are shown respectively behind the wheeled worktables 21 in the figure and each of the operators m assembles parts on the operation chart board on the wheeled worktable 21 on arrival of the wheeled worktable 21 at the position of the operator m.
Both the turning parts 25 and 26 are simply places for directional changes of the wheeled worktables 21, and no work is done there. An entrance 27 for finished products from a previous process is built on the outbound passage side of the turning part 26 while an exit 28 for the finished product in this assembly line is built on the return passage side.
In such an assembly line, classified flow process operations are carried out for efficient manufacturing of the wire harnesses.
However, the following problems exist in the conventional assembly line in the form as described above.
(1) In a case of change in production mode (production amount or production model) as the object of line manufacturing, the aforenamed wheeled worktables 21 need to be increased or thinned out and, for this purpose, the above-described assembly line form wherein the chain 22 is secured along the conveyance passage of the wheeled worktables 21 requires a large scale of remodeling of the transportation mechanism, through replacement or cut of the chain 22 but the work requires a lot of human power, and requires the assembly line to stop for a long time.
It may be convenient if the conveyance passage is large enough to allow any immediate increase in the wheeled worktables, but this can cause increase in the pitch of spacing between the wheeled worktables, which can result in decrease in conveyance efficiency and, accordingly, decrease in production efficiency.
In case the wheeled worktables are thinned out under this circumstance, the spacing pitch between the wheeled worktables becomes larger and the assembly line production efficiency becomes lower.
Moreover, this is a great loss in the aspect of the site use efficiency.
(2) In a case of replacing only the wheeled worktables 21 for a reason of change in the model to be manufactured, even without changes in the production amount as the object of manufacturing and accordingly without increase or decrease in the number of the wheeled worktables 21, the assembly line stagnates greatly since it gives trouble and takes time to dismount from and mount on the chain 22.
(3) In a case of loss in the chain 22 or a malfunction of the drive motor MC, it gives trouble and takes time for the recovery, and, in general, it costs a lot for the repair.
Moreover, this is a great loss in the aspect of the site use efficiency.
(2) In a case of replacing only the wheeled worktables 21 for a reason of change in the model to be manufactured, even without changes in the production amount as the object of manufacturing and accordingly without increase or decrease in the number of the wheeled worktables 21, the assembly line stagnates greatly since it gives trouble and takes time to dismount from and mount on the chain 22.
(3) In a case of loss in the chain 22 or a malfunction of the drive motor Mc, it gives trouble and takes time for the recovery, and, in general, it costs a lot for the repair.
Therefore, the invention is purposed to solve the above-described problems in the conventional wire harness assembly line, making the assembly line in the form that can afford any change in the assembly line configuration on rise of any need for change in the production amount and/or in such the production form, such as the model, and that can afford the change without troublesome operations and at low costs, with successful prevention of any decrease in the assembly line conveyance efficiency, or accordingly any decrease in the production efficiency.
To solve the above-described problems, the invention has a structure wherein each of the wheeled worktables travels self-dependently with drive of a motor while being isolated from the others and wherein each of the wheeled worktables is equipped with a sensor for travel along predetermined conveyance passage on a floor while objects of recognition by the sensor are installed along the predetermined route on the floor surface.
The structure enables assembly line change only with replacement of the sensor recognition objects and rerouting of the wheeled worktable conveyance passage. The recognition object of the sensor is usually an optical recognition tape or a magnetic recognition tape that is attached to a floor where the wheeled worktables travel and that is easy to be attached and removed. Since the conveyance route can be modified into any desired form only by the tape replacement, an optimum rerouting that eliminate every unnecessary space between adjacent wheeled worktables with setting of a maximum conveyance efficiency (accordingly the production efficiency) is available at any increase or decrease in the wheeled worktable number. Moreover, the cost is small.
Additionally, such is a desirable configuration that a rectangle whose center line is parallel to a travelling direction of the wheeled worktable is defined on the bottom surface of the wheeled worktable while an isosceles triangle whose base and height are equal is defined in such manner that an symmetry axis thereof overlaps the center line of the rectangle with the base including a midpoint of the rectangle and by that a driving wheel that has a steering function is disposed at a vertex of the isosceles triangle while trailing wheels are securely disposed at both ends of the base in such manner that the revolving surfaces thereof are always in a direction parallel to the travelling direction of the wheeled worktable. As shown in FIG. 6 below and FIGS. 8 through 10 as its comparison examples, this configuration enables reduction of the entire assembly line size since the turnabout of the wheeled worktable at the turning part of the assembly line can be carried out most efficiently with a small turn to result with reduction in the space occupation at the turning part.